Impulsivity is a construct thought to be related to substance abuse. The present project proposes to assess impulsivity from multiple perspectives and to examine the relationship between impulsivity, drug abuse, and HIV risk-behaviors. The hypotheses are that (1) drug abusers will demonstrate increased impulsivity to controls, (2) active drug abusers will demonstrate greater impulsivity than treated, currently abstinent drug abusers, (3) impulsivity may vary across different types of drug users: heroin, cocaine, and alcohol abusers, and (4) impulsivity may be associated with HIV risk-taking behaviors.